1. Field of the Invention
The present invention relates to a laser cutting method and a laser cutting apparatus for cutting two substrates disposed one over the other and bonded to each other, such as a liquid crystal panel, and a method and an apparatus for manufacturing a liquid crystal device.
2. Description of the Related Art
In a manufacturing process for a liquid crystal panel, a large number of products are taken out of one glass substrate. In this case, the glass substrate must be cut and separated to fit a liquid crystal panel to a product size.
FIG. 14 is an explanatory view for illustrating a conventional cutting method for fitting a liquid crystal panel to a product size. On the surface of one glass substrate 1 of two glass substrates 1 and 2, which are bonded to each other via a sealing material 3 for sealing liquid crystal, a scribe line 5 is formed with, for example, a diamond tip. After the two glass substrates 1 and 2 are turned over, a bending stress is applied from the surface of the other glass substrate 2 by using a jig such as a rubber roller so as to cut two glass substrates 1 and 2.
However, in the conventional cutting method as described above, the start point of a crack on the scribe line appears unstably, and the glass substrates are cut discontinuously, so that many chippings are produced. If many chippings are produced, cleaning must be performed to remove the chippings. Also, because this method is of a contact cutting mode, any foreign matter sticking on the rubber roller may scratch the glass substrate 2. Also, because the destructive power by the rubber roller is low, the glass substrates including the sealing material 3 cannot be cut, so that cutting must be performed at an area without the sealing material 3. Therefore, as shown in portion A of FIG. 15, a cleaning solution (liquid for cleaning liquid crystal which wets the glass substrates when it is enclosed) remains undesirably between the glass substrate 1 and the glass substrate 2 in the vicinity of the sealing material 3. Since the cleaning solution reacts with wiring of the liquid crystal panel, it is necessary to remove the cleaning solution.
Also, a method in which a laser beam is employed to cut a glass substrate etc. has been proposed (for example, Japanese Patent Laid-Open No. 11-104869 specification). However, this cutting method has been premised to cut one substrate, not to cut two substrates. Even if an attempt is made to cut two substrates by this method, they cannot be cut under the same conditions. Although they can be cut by increasing laser power (or decreasing cutting speed), such a method has problems of low cutting accuracy (linearity) and no reproducibility. These problems will be explained in further detail.
In the case of cutting one substrate with a laser beam, an internal stress due to heat is utilized. In the case of cutting two substrates, the following problems arise:
(1) A thermal stress acts in the upper glass substrate only. This is because glass has a high light absorption coefficient, so that only the upper glass substrate is heated, and the lower glass substrate is not heated.
(2) The upper and lower glass substrates are connected to each other by the sealing material (see FIG. 14), and so that when the upper glass substrate is going to crack, the lower glass substrate serves to restrain the cracking of the upper glass substrate. Accordingly, two substrates cannot be cut under the same conditions of cutting one glass substrate.
(3) Although force to cut the upper glass substrate can be increased by increasing thermal energy, the lower glass substrate is cut by receiving the force via the sealing material. However, the received force depends on the construction of panel, the bonding state of sealing material, etc. and has no reproducibility.
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to provide a laser cutting method and a laser cutting apparatus, and a method and an apparatus for manufacturing a liquid crystal device, in which a plurality of substrates disposed one over another, especially two substrates disposed one over the other and bonded to each other, can be cut with higher accuracy.
(1) One mode of the present invention provides a laser cutting method in which a laser beam is applied to a pair of opposed substrates to cut the paired substrates, including at least the steps of applying a first laser beam from a first surface side of one substrate of the paired substrates; and applying a second laser beam from a second surface side of the other substrate of the paired substrates. In the present invention, laser beams are applied to both surfaces of the paired substrates. When a laser beam is applied, the temperature of the irradiated location rises, so that a thermal stress developed by the temperature gradient increases. Therefore, a crack is generated on each of the substrates in the thickness direction, so that a high cutting accuracy (linearity) and excellent reproducibility is provided. Also, since the substrates are cut in a non-contact mode, there is no fear of scratching the substrates like the prior art. In this case, if the step of applying the first laser beam and the step of applying the second laser beam are carried out at the same time, the working time can be shortened.
(2) In the laser cutting method in accordance with another mode of the present invention, scribe lines are formed in advance at cutting locations on the substrates, and the laser beams are applied to the scribelines. In the present invention, when the laser beams are applied to the scribe lines, the temperature of the irradiated location rises, so that a thermal stress developed by the temperature gradient increases. Therefore, cracks originating at the scribe lines develop in the thickness direction to break the substrates, so that the cutting accuracy (linearity) is further enhanced.
(3) In the laser cutting method in accordance with still another mode of the present invention, the pair of substrates and the laser beams are moved relatively to cut the pair of substrates. To do this, there can be used a method in which a position of the pair of substrates is fixed and the laser beams are moved along the scribe lines, or a method in which locations irradiated with the laser beams are fixed and a work support section supporting the pair of substrates is moved. In the present invention, cracks originating at the scribe lines develop in the thickness direction, and the cracks propagate along with the relative movement of the laser beams, by which the pair of substrates is cut along the scribe lines.
(4) In the laser cutting method in accordance with still another mode of the present invention, further in the laser cutting method of the above item (3), correlation between a relative moving speed of the laser beams to the pair of opposed substrates and a power density of the laser beams is set in a predetermined range. If the relative speed of the laser beams is low and the power density of the laser beams is high, the substrate is destroyed. If the relative speed of the laser beams is high and the power density of the laser beams is low, the substrate cannot be cut. In the present invention, therefore, the relative speed of the laser beams and the power density of the laser beams are set so that the correlation therebetween is in a predetermined range in order for the substrate to be cut properly.
(5) In the laser cutting method in accordance with still another mode of the present invention, further in the laser cutting method of any one of the above items (1) to (4), upper and lower substrates are cut including another member, for example, a sealing material, interposed between the pair of opposed substrates. In the present invention, since a laser beam is applied to each of both surfaces of the two substrates, the substrates having another member (including the later-described sealing material and bonding layer) interposed therebetween can be cut.
(6) In the laser cutting method of any one of the above items (1) to (5), objects to cut include a substrate consisting of a glass-based or crystal-based member.
(7) In the laser cutting method in accordance with still another mode of the present invention, further in the laser cutting method of any one of the above items (1) to (6), a laser having a high energy absorption coefficient with respect to a substrate to cut, for example, a CO2 laser or a YAG laser, is used to cut the substrate. By using such a laser corresponding to the substrate, the cutting operation can be performed efficiently.
(8) One mode of the present invention provides a laser cutting apparatus in which a laser beam is applied to a pair of opposed substrates to cut the paired substrates, comprising at least a laser oscillator for emitting a laser beam; and an irradiation mechanism for applying the laser beam to a cutting location of the paired substrates.
(9) In the laser cutting apparatus in accordance with another mode of the present invention, the laser beam is branched into a plurality of beams, and the branched beams are applied to a plurality of locations on the paired substrates, by which the plurality of locations on the substrates can be cut at the same time. According to the present invention, the plurality of locations (a plurality of lines) on the substrates can be cut at the same time.
(10) In the laser cutting apparatus in accordance with still another mode of the present invention, the laser cutting apparatus further comprises a first irradiation mechanism for applying a first laser beam from the first surface side of one substrate of the paired substrates; and a second irradiation mechanism for applying a second laser beam from the second surface side of the other substrate of the paired substrates. Also, the laser cutting apparatus further comprises a beam condensing device for condensing and applying the first and second laser beams to the cutting locations on the substrates.
(11) In the laser cutting apparatus in accordance with still another mode of the present invention, the laser cutting apparatus further comprises laser branching means for branching each of the first and second laser beams into a plurality of beams, and a beam condensing device for condensing and applying the branched beams to the cutting locations on the substrates. According to the apparatus of the present invention, a plurality of locations (a plurality of lines) on the substrates can be cut at the same time.
(12) In the laser cutting apparatus in accordance with still another mode of the present invention, the laser cutting apparatus further comprises a mechanism for relatively moving the substrates and the laser beams along scribe lines formed at the cutting locations of the substrates. This mechanism may consist of a substrate movement mechanism comprising a work support section for supporting the paired substrates, an X slide mechanism for moving the work support section in the X direction, and a Y slide mechanism for moving the work support section in the Y direction. Also, this mechanism may consist of a scanning device for moving the laser beams.
(13) In the laser cutting apparatus in accordance with still another mode of the present invention, the relative movement of the laser beam with respect to the substrates is controlled based on the relationship between the relative speed of the laser beams with respect to the substrates and the power density of the laser beams.
(14) In the laser cutting apparatus in accordance with still another mode of the present invention, the laser cutting apparatus further comprises a CO2 laser used for glass-based or crystal-based substrates and/or a YAG laser used for silicon-based substrates.
(15) One mode of the present invention provides a method for manufacturing a liquid crystal device, comprising the steps of bonding a pair of opposed substrates to each other; and applying a first laser beam from the first surface side of one substrate of the paired substrates and applying a second laser beam from the second surface side of the other substrate of the paired substrates.
(16) In the method for manufacturing a liquid crystal device in accordance with another mode of the present invention, the liquid crystal device is made by bonding a pair of opposed substrates to each other via a sealing material, and the pair of substrates including the sealing material is cut. Thereby, a state in which cleaning solution remains in the vicinity of a sealing portion can be avoided.
(17) In the method for manufacturing a liquid crystal device in accordance with still another mode of the present invention, each of the first and second laser beams is branched into a plurality of beams, and the branched beams are applied to a plurality of locations on each surface of the substrates to cut the substrates at the plurality of locations at the same time. According to the present invention, the plurality of locations (a plurality of lines) on the substrates of the liquid crystal device can be cut at the same time.
(18) In the method for manufacturing a liquid crystal device in accordance with still another mode of the present invention, after liquid crystal is injected between the pair of substrates, the paired substrates are cut.
(19) In the method for manufacturing a liquid crystal device in accordance with still another mode of the present invention, after the paired substrates are cut by the laser beams, liquid crystal is injected.
(20) One mode of the present invention provides an apparatus for manufacturing a liquid crystal device, by which a liquid crystal device constructed by holding liquid crystal between a pair of opposed substrates is manufactured, comprising at least a laser oscillator; and an irradiation mechanism for applying a laser beam emitted from the laser oscillator to the paired substrates.
(21) In the apparatus for manufacturing a liquid crystal device in accordance with another mode of the present invention, the apparatus further comprises a first irradiation mechanism for applying a first laser beam from the first surface side of one substrate of the paired substrates; and a second irradiation mechanism for applying a second laser beam from the second surface side of the other substrate of the paired substrates.
(22) In the apparatus for manufacturing a liquid crystal device in accordance with still another mode of the present invention, the apparatus further comprises a work support section for supporting the paired substrates, and the work support section has an opening penetrating the work support section. A plurality of the openings having a slender shape may be formed in the work support section.
(23) In the apparatus for manufacturing a liquid crystal device in accordance with still another mode of the present invention, the irradiation mechanism includes a moving device for moving the paired substrates and/or a scanning device for moving the laser beams.
(24) In the apparatus for manufacturing a liquid crystal device in accordance with still another mode of the present invention, the apparatus further comprises laser branching means for branching each of the first and second laser beams into a plurality of beams.